Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk typically comprises a number of concentric data tracks each partitioned into a number of data sectors. Access operations are performed by seeking the head to a target data track, and performing a write/read operation on the data sectors within the data track. The disk typically comprises embedded servo sectors having position information recorded therein, such as coarse position information (e.g., a track address) and fine position information (e.g., servo bursts). A servo controller processes the servo sectors to position the head over the target data track.
The data sectors are typically scanned for defects, for example, during a manufacturing process or while the disk drive is in the field. The defect procedure typically involves writing a test pattern to a data sector, reading the test pattern from the data sector, and processing the read signal to detect a defect relative to a defect threshold. If the data sector is determined to be defective, it is typically “mapped out” by either skipping the data sector (sector slipping), or by remapping a logical block address (LBA) associated with the defective data sector to a spare data sector (relocating the data sector). Data sectors may also be mapped out if a defect is detected in one or more of the embedded servo sectors, for example, by mapping out the data sectors of an entire or partial data track.
It is desirable to verify that a sector is actually defective before mapping out one or more data sectors since mapping out data sectors decreases the capacity as well as the performance of the disk drive. However, it is also desirable to ensure defective sectors are not missed in order to avoid catastrophic data loss while the disk drive is in the field.